The invention relates to an auxiliary frame for a motor vehicle as well as a method of assembly of such an auxiliary frame.
An auxiliary frame for a motor vehicle that is formed as a subframe, which is also described as axle support, is generally known and is regularly used as a drive unit carrier, which is screwed to the vehicle body via corresponding connection sites, i.e., to the longitudinal members of the vehicle body as well as for example to joint sites of the A-pillar that are situated at the floor. Such auxiliary frames can be used both in the region of the front axles and in the region of the rear axles.
From DE 10 2011 101 408 A1 a generic auxiliary frame for a motor vehicle is known, which for example has a rectangular-shaped closed frame, in which the front and rear cross members as well as the lateral longitudinal members are connected to each other via joint elements such as aluminum cast joints. At the front and rear cast joints, respective connection points are provided to screw the auxiliary frame to the vehicle body. Additionally, further functions are integrated at the front and rear cast joints, for example control arm consoles for the control arms of the wheel suspension. The auxiliary frame known from DE 10 2011 101 408 A1 also includes a reinforcement element that is designed as a cross strut, within which the rear cast joints may be formed integrally. At its front end the reinforcement element is connected at first connection sites, for example threaded bushings, to the front cast joints. The two front cast joints are furthermore connected to each other via the front cross member. The front cross member is arranged with a longitudinal offset before the above mentioned first connection sites (or before the reinforcement element). Especially in the region of the front cross member high forces are introduced during operation. As a result a the front cross member has to be constructed using a great amount of material, i.e., so as to have great wall thicknesses, to meet component stiffness requirements.